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  • Oceans are an important reservoir of CO2, absorbing a significant quantity of CO2 (one-third) produced by man-made activities and thus effectively act as a buffer to climate change. However, due to the increasing absorption of CO2 by the ocean waters, ocean acidification takes place.
  • Ocean acidification refers to the change in ocean chemistry from basic to acidic due to the intake of carbon compounds from the atmosphere.
  • Currently, oceans have pH value (indicator of acidic or basic nature) of around 8 (basic in nature). However, this pH is reducing towards acidic nature.
  • Excess CO2 in ocean waters react with water to form carbonic acid. The chemical reaction can be described as follows:
  • Water (H2O) + Carbon Dioxide (CO2) Carbonic Acid (H2CO3)
  • Further, carbonic acid (H2CO3) breaks into hydrogen ions (H+) and bicarbonate ions (HCO3).

Factors Which Influence Ocean Acidification 

Apart from high CO2 emissions in the atmosphere, the following factors lead to ocean acidification:


  • It relates to a condition of excess nutrients in water bodies. It leads to the growth of algae (in large amount) on the surface of water bodies.
  • Growth of algae reduces the absorption of sunlight in water bodies.
  • Reduced availability of sunlight hampers photosynthesis causing reduction of oxygen in the water body and death of marine organisms.
  • Dead marine organisms sink at the bottom of the water body, where they are decomposed by bacteria.
  • Bacteria engage in respiration and further reduce the oxygen level in the water body, resulting in acidification.

Acid Rain:

  • Addition of acid rainwater leads to acidification of water body.

Impact of Ocean Acidification on Calcium Carbonate Shells of Marine Life

  • Ocean acidification increases the concentration of H+ ions (acidic substances have higher concentration of H+ ions).
  • The H+ ions facilitate bicarbonate ions (HCO3) in place of carbonate ions (CO32-).
  • Carbonate ions are essential for certain marine organisms for building their calcium carbonate (CaCO3) shells and skeletons.
  • However, ocean acidification increases the concentration of carbonic acid resulting in the formation of bicarbonate ions and causes decrease in the concentration of carbonate ions. Thus, marine organisms are not able to form shells leading to their early death.
  • The dead bodies of marine species remain deposited at the continental shelves.
  • This deposition cause frequent upwelling currents resulting in the movement of deep cold water at the ocean surfaces.
  • In deei cold ocean waters, CO2 is higher, and thus there is absence of carbonate ions, causing further dissolution of CaCO3 shells.
  • On the other hand, surface waters possess large amount of CO32- ions because of highe concentration of oxygen.

Environment & Biodiversity

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